Unicast, Multicast, Broadcast and Anycast
IP communication is classified by how the destination is addressed.
Unicast
One-to-one. Almost all normal traffic — web, email — is unicast.
Multicast
One-to-a-group. Sent to 224.0.0.0/4, used for IPTV or market-data feeds where the same stream goes to many receivers efficiently.
Broadcast
One-to-everyone on the local segment, e.g. 255.255.255.255. Used by ARP and DHCP discovery. IPv6 has no broadcast and uses multicast instead.
Anycast
One-to-the-nearest. The same IP is announced from many locations, and routing delivers to the closest. Used by DNS root servers, CDNs, and 8.8.8.8 (Google Public DNS).
| Cast | Destination | Example |
|---|---|---|
| Unicast | One host | Web / email |
| Multicast | A group | Video streaming |
| Broadcast | All (same LAN) | DHCP / ARP |
| Anycast | Nearest one | DNS / CDN |